ABSTRACT The application of immunotherapy to cancer has yielded impressive and inspiring results. However, these results seem to only apply to a subset of patients. Many practitioners and researchers are aiming to discover why there are differential responses from patients. Yet existing techniques to characterize cancer do not focus on the immune response itself. Therefore, we aim to fill this gap with a technology that directly characterizes the cancer in terms of its immune response. To do this, we will use a core technology, developed in our labs, that utilizes magnetic nanoparticles to enrich and activate cancer targeting CD8+ T cells to detectable and, potentially even, therapeutic levels. Specifically, we will look for neoepitopes?epitopes generated by the mutations of the cancer itself that can generate an immune response. We have demonstrated feasibility of this approach within both murine and human contexts; however, we have yet to develop the assay into a high- throughput approach that covers a broad heterogenous human population. To do so, we will first engineer the magnetic nanoparticles, called artificial antigen-presenting cells (aAPCs) because they have both an antigen- loaded human leukocyte antigen (HLA) and co-stimulatory molecules on their surface. Engineering parameters will include size, ligand density, and ligand choice. Furthermore, we will extend output by developing a 96-well plate high-throughput version of the assay. We will also broaden the reach of this technology by developing aAPCs for additional class I HLA alleles and also for an aAPC for CD4+ T cell stimulation. Finally, through our collaborative efforts with Dr. Jeff Weber at NYU, we will validate the technology by measuring and detecting neoepitopes from stage IV melanoma patients. We will assess how treatment affects the immune response to the tumor by probing before and after checkpoint blockade therapy. This technology will fill the gap of providing an immunological characterization of cancer in both murine models and critically in patients with cancer. This representation will shape both how therapy is delivered and how the next generation of therapies are developed.